The goals of this project are to determine the major features of synaptic plasticity and functional circuitry in the electrosensory lobe (ELL) of mon-nyrid electric fish. The ELL is a cerebellum-like structure where the primary afferent fibers from electroreceptors terminate. The ELL and similar cerebellum-like structures in other fish are adaptive sensory processors in {Date Released: 08/08/1997 Date Printed: 01/15/1998} which memory-like predictions about sensory input are generated and subtracted from current sensory input, allowing the neural responses to unexpected or novel input to stand out more clearly. The predictions are based on prior associations between sensory input and various central signals conveyed by parallel fibers such as corollary discharge signals linked to motor commands. Plasticity at the excitatory synapse between parallel fibers and ELL cells could be the cellular mechanism for the generation of these predictions about sensory input, and such plasticity has now been demonstrated in the in vitro slice preparation by the P.I. and his colleagues. The plasticity is observed after a few minutes of pairing of a presynaptic parallel presynaptic parallel fiber input with a postsynaptic spike. The plasticity is observed after a few minutes of pairing of a presynaptic parallel fiber input with a postsynaptic spike. The plasticity is anti-Hebbian in that pairings in which the postsynaptic spike occurs during the parallel fiber-evoked epsp lead to a depression of the epsp, whereas pairings at other delays lead to enhancement. Indications of associative plasticity at inhibitory synapses were also obtained. This project is focused on the mechanisms and features of these different forms of synaptic plasticity and on the functional circuitry of ELL. ELL cells will be recorded intracellularly in the in vitro slice preparation. The roles of NMDA receptors, nitric oxide, postsynaptic spikes and postsynaptic calcium will be examined along with the effects of various pairing protocols. Circuitry will be investigated both morphologically and functionally at the cell to cell level. The results are expected to enhance our understanding of synaptic plasticity at the cellular level and the role of such plasticity in memory-like functions such as the generation of predictions about sensory input.